textproduct: Albany

WHAT HAS CHANGED

No major changes but there is now a low chance for an isolated tornado in the mid-Hudson Valley and southern Taconics today.

KEY MESSAGES

1) A slow moving cold front will continue to support periods of showers and thunderstorms across the entire region through early this morning. Heavy rainfall rates can result in isolated to scattered flash flooding, with areas that recently received high rainfall amounts most susceptible to renewed flooding.

2) There is a marginal risk (level 1 of 5) for severe thunderstorms this afternoon for much of eastern NY and western New England, except the southwest Adirondacks and Mohawk Valley. Damaging winds are the primary hazard but there is a low chance for an isolated tornado in the mid-Hudson Valley and southern Taconics.

DISCUSSION

KEY MESSAGE 1...

Latest water vapor imagery shows a deep fetch of moisture streaming from the Gulf and western Atlantic northward into the Northeast ahead of an amplifying shortwave trough tracking into the Saint Lawrence River Valley. There is good consensus that the trough starts to take on a negative tilt towards 12 UTC and with a jet streak strengthening over the Northeast, strong lift and upper level divergence overlapping such a moisture rich environment will help amplify rainfall rates across eastern NY and western New England through early this morning. Forecast soundings also show the classic tall/skinny CAPE profile with high freezing heights supporting efficient warm rain processes and potential for high rainfall rates across the region. Latest HREF shows a southwest to northeast oriented ribbon of medium to high probabilities for 3-hrly rainfall amounts from 09 to 15 UTC exceeding 1" focused in the mid-Hudson Valley into NW CT and New England. There is even low probabilities for over 2" of rain in a 3-hr period during this window. This matches the slight risk (level 2 of 4) Day 1 ERO placement and will feature the highest chance for high rainfall rates to result in isolated to scattered instances of flash flooding. They also show a veering wind profile with south to southwesterly winds extending through a deep layer with small corfidi vectors indicating potential for backbuilding heavy rainfall early this morning. While the mid- Hudson Valley into NW CT and parts of western MA missed out on the extreme rainfall from last week, the risk for flash flooding will nonetheless increase should heavy rainfall rates persist over a given area. Luckily, the incoming trough will limit the duration of the high rainfall rates and help shift it further into New England by 15 - 18 UTC, decreasing the potential for widespread flash flooding issues. Total rainfall amounts through 15 UTC Monday across eastern NY and western New England from the latest HREF PMM guidance shows potential for 0.5 to 2 inches with locally higher amounts likely where heavy rain can persist.

After the main area of widespread rain exits into New England by mid-morning, we enter into a brief break before the main trough axis and sfc cold front swings through from west to east by 15 - 21 UTC. Should sufficient breaks of sun or thinning of cloud coverage occur, the environment will destabilize further. CAMs are in good agreement with a line of convection developing ahead of the sfc boundary and tracking eastward through the afternoon. Strong low-level convergence ahead of the front will help focus moisture and lift, likely supporting additional periods of heavy rain. Areas that have already become saturated from the overnight/early morning rainfall will be more vulnerable to localized flooding but given the progressive nature of the front and any convection, any additional flooding should be isolated/localized.

KEY MESSAGE 2...

There looks to be a small window of opportunity from mid- morning through early to mid afternoon for clouds to thin enough or even briefly break for insolation. Given the very moist environment including dew points in the upper 60s to even low 70s today, any insolation will easily contribute to increased sfc-based instability with CAMs showing 1000 - 2000J/kg developing mainly along and east of the Hudson River into western New England where there should a longer delay before the front arrives. Strong dynamics/lift ahead of the negatively tilted trough will support strong southerly winds through the column with veering winds in the low-levels also supporting directional shear. This favors a high shear, low/modest CAPE environment with the latest guidance in good agreement with impressive deep layer shear amounts ranging 40 to 50kts ahead of the boundary. This can easily support organized convection and allow updrafts to grow upscale, should instability be sufficient. The latest probabilities for strong 2-5km updraft helicity values from the HREF are rather low at only 10-20% as the front pushes through this afternoon suggesting the atmosphere may not have enough time to destabilize between the exiting heavy rain and incoming convective line. However, the impressive shear and strong dynamics aloft are reasons to maintain a watchful eye on thunderstorms through this afternoon even if they remain low topped as they can still become strong to severe and produce damaging winds should any updrafts become tall enough. The SPC Day 1 Convective Outlook continues to show the marginal risk (level 1 of 5) from Hudson River eastward into western New England but now includes a low chance (2%) chance for an isolated tornado given low-level directional shear and veering winds.

Winds behind the cold front this afternoon will turn gusty and shift to the west reaching up to 25-30kts per forecast soundings as cool/much drier air advect into the region. Dew points will noticeably drop tonight into tomorrow bringing relief from the uncomfortable humidity.

AVIATION /12Z MONDAY THROUGH FRIDAY/

Through 12Z Tuesday... MVFR conditions prevail at ALB, PSF, and GFL this morning while POU cigs should trend downwards from VFR to MVFR this morning. The widespread rain is already exiting into New England but MVFR cigs look to persist through 17-18 UTC. Then, a line of scattered showers and thunderstorms develop ahead of a cold front between 16 and 20 UTC at all terminals. Any heavier shower or storm can result in vis and cigs dropping to MVFR/IFR briefly with brief stronger winds out of the west- northwest. This is reflected in PROB30 groups. Winds then shift to the west or west-northwest by the late afternoon hours behind the cold front with gusts peaking around 20-30 kts before weakening after sunset. Thereafter, widespread VFR conditions and clearing skies are expected over the final several hours of this TAF period.

Outlook...

Tuesday Night: No Operational Impact. NO SIG WX. Wednesday: No Operational Impact. NO SIG WX. Wednesday Night: Low Operational Impact. Slight Chance of SHRA. Thursday: High Operational Impact. Likely SHRA...TSRA. Thursday Night: Moderate Operational Impact. Chance of SHRA...TSRA. Friday: High Operational Impact. Likely SHRA...TSRA. Friday Night: Moderate Operational Impact. Chance of SHRA...TSRA. Saturday: Moderate Operational Impact. Chance of SHRA...TSRA.

ALY WATCHES/WARNINGS/ADVISORIES

CT...None. NY...None. MA...None. VT...None.